1/* 2 * reserved comment block 3 * DO NOT REMOVE OR ALTER! 4 */ 5/* 6 * jfdctflt.c 7 * 8 * Copyright (C) 1994-1996, Thomas G. Lane. 9 * This file is part of the Independent JPEG Group's software. 10 * For conditions of distribution and use, see the accompanying README file. 11 * 12 * This file contains a floating-point implementation of the 13 * forward DCT (Discrete Cosine Transform). 14 * 15 * This implementation should be more accurate than either of the integer 16 * DCT implementations. However, it may not give the same results on all 17 * machines because of differences in roundoff behavior. Speed will depend 18 * on the hardware's floating point capacity. 19 * 20 * A 2-D DCT can be done by 1-D DCT on each row followed by 1-D DCT 21 * on each column. Direct algorithms are also available, but they are 22 * much more complex and seem not to be any faster when reduced to code. 23 * 24 * This implementation is based on Arai, Agui, and Nakajima's algorithm for 25 * scaled DCT. Their original paper (Trans. IEICE E-71(11):1095) is in 26 * Japanese, but the algorithm is described in the Pennebaker & Mitchell 27 * JPEG textbook (see REFERENCES section in file README). The following code 28 * is based directly on figure 4-8 in P&M. 29 * While an 8-point DCT cannot be done in less than 11 multiplies, it is 30 * possible to arrange the computation so that many of the multiplies are 31 * simple scalings of the final outputs. These multiplies can then be 32 * folded into the multiplications or divisions by the JPEG quantization 33 * table entries. The AA&N method leaves only 5 multiplies and 29 adds 34 * to be done in the DCT itself. 35 * The primary disadvantage of this method is that with a fixed-point 36 * implementation, accuracy is lost due to imprecise representation of the 37 * scaled quantization values. However, that problem does not arise if 38 * we use floating point arithmetic. 39 */ 40 41#define JPEG_INTERNALS 42#include "jinclude.h" 43#include "jpeglib.h" 44#include "jdct.h" /* Private declarations for DCT subsystem */ 45 46#ifdef DCT_FLOAT_SUPPORTED 47 48 49/* 50 * This module is specialized to the case DCTSIZE = 8. 51 */ 52 53#if DCTSIZE != 8 54 Sorry, this code only copes with 8x8 DCTs. /* deliberate syntax err */ 55#endif 56 57 58/* 59 * Perform the forward DCT on one block of samples. 60 */ 61 62GLOBAL(void) 63jpeg_fdct_float (FAST_FLOAT * data) 64{ 65 FAST_FLOAT tmp0, tmp1, tmp2, tmp3, tmp4, tmp5, tmp6, tmp7; 66 FAST_FLOAT tmp10, tmp11, tmp12, tmp13; 67 FAST_FLOAT z1, z2, z3, z4, z5, z11, z13; 68 FAST_FLOAT *dataptr; 69 int ctr; 70 71 /* Pass 1: process rows. */ 72 73 dataptr = data; 74 for (ctr = DCTSIZE-1; ctr >= 0; ctr--) { 75 tmp0 = dataptr[0] + dataptr[7]; 76 tmp7 = dataptr[0] - dataptr[7]; 77 tmp1 = dataptr[1] + dataptr[6]; 78 tmp6 = dataptr[1] - dataptr[6]; 79 tmp2 = dataptr[2] + dataptr[5]; 80 tmp5 = dataptr[2] - dataptr[5]; 81 tmp3 = dataptr[3] + dataptr[4]; 82 tmp4 = dataptr[3] - dataptr[4]; 83 84 /* Even part */ 85 86 tmp10 = tmp0 + tmp3; /* phase 2 */ 87 tmp13 = tmp0 - tmp3; 88 tmp11 = tmp1 + tmp2; 89 tmp12 = tmp1 - tmp2; 90 91 dataptr[0] = tmp10 + tmp11; /* phase 3 */ 92 dataptr[4] = tmp10 - tmp11; 93 94 z1 = (tmp12 + tmp13) * ((FAST_FLOAT) 0.707106781); /* c4 */ 95 dataptr[2] = tmp13 + z1; /* phase 5 */ 96 dataptr[6] = tmp13 - z1; 97 98 /* Odd part */ 99 100 tmp10 = tmp4 + tmp5; /* phase 2 */ 101 tmp11 = tmp5 + tmp6; 102 tmp12 = tmp6 + tmp7; 103 104 /* The rotator is modified from fig 4-8 to avoid extra negations. */ 105 z5 = (tmp10 - tmp12) * ((FAST_FLOAT) 0.382683433); /* c6 */ 106 z2 = ((FAST_FLOAT) 0.541196100) * tmp10 + z5; /* c2-c6 */ 107 z4 = ((FAST_FLOAT) 1.306562965) * tmp12 + z5; /* c2+c6 */ 108 z3 = tmp11 * ((FAST_FLOAT) 0.707106781); /* c4 */ 109 110 z11 = tmp7 + z3; /* phase 5 */ 111 z13 = tmp7 - z3; 112 113 dataptr[5] = z13 + z2; /* phase 6 */ 114 dataptr[3] = z13 - z2; 115 dataptr[1] = z11 + z4; 116 dataptr[7] = z11 - z4; 117 118 dataptr += DCTSIZE; /* advance pointer to next row */ 119 } 120 121 /* Pass 2: process columns. */ 122 123 dataptr = data; 124 for (ctr = DCTSIZE-1; ctr >= 0; ctr--) { 125 tmp0 = dataptr[DCTSIZE*0] + dataptr[DCTSIZE*7]; 126 tmp7 = dataptr[DCTSIZE*0] - dataptr[DCTSIZE*7]; 127 tmp1 = dataptr[DCTSIZE*1] + dataptr[DCTSIZE*6]; 128 tmp6 = dataptr[DCTSIZE*1] - dataptr[DCTSIZE*6]; 129 tmp2 = dataptr[DCTSIZE*2] + dataptr[DCTSIZE*5]; 130 tmp5 = dataptr[DCTSIZE*2] - dataptr[DCTSIZE*5]; 131 tmp3 = dataptr[DCTSIZE*3] + dataptr[DCTSIZE*4]; 132 tmp4 = dataptr[DCTSIZE*3] - dataptr[DCTSIZE*4]; 133 134 /* Even part */ 135 136 tmp10 = tmp0 + tmp3; /* phase 2 */ 137 tmp13 = tmp0 - tmp3; 138 tmp11 = tmp1 + tmp2; 139 tmp12 = tmp1 - tmp2; 140 141 dataptr[DCTSIZE*0] = tmp10 + tmp11; /* phase 3 */ 142 dataptr[DCTSIZE*4] = tmp10 - tmp11; 143 144 z1 = (tmp12 + tmp13) * ((FAST_FLOAT) 0.707106781); /* c4 */ 145 dataptr[DCTSIZE*2] = tmp13 + z1; /* phase 5 */ 146 dataptr[DCTSIZE*6] = tmp13 - z1; 147 148 /* Odd part */ 149 150 tmp10 = tmp4 + tmp5; /* phase 2 */ 151 tmp11 = tmp5 + tmp6; 152 tmp12 = tmp6 + tmp7; 153 154 /* The rotator is modified from fig 4-8 to avoid extra negations. */ 155 z5 = (tmp10 - tmp12) * ((FAST_FLOAT) 0.382683433); /* c6 */ 156 z2 = ((FAST_FLOAT) 0.541196100) * tmp10 + z5; /* c2-c6 */ 157 z4 = ((FAST_FLOAT) 1.306562965) * tmp12 + z5; /* c2+c6 */ 158 z3 = tmp11 * ((FAST_FLOAT) 0.707106781); /* c4 */ 159 160 z11 = tmp7 + z3; /* phase 5 */ 161 z13 = tmp7 - z3; 162 163 dataptr[DCTSIZE*5] = z13 + z2; /* phase 6 */ 164 dataptr[DCTSIZE*3] = z13 - z2; 165 dataptr[DCTSIZE*1] = z11 + z4; 166 dataptr[DCTSIZE*7] = z11 - z4; 167 168 dataptr++; /* advance pointer to next column */ 169 } 170} 171 172#endif /* DCT_FLOAT_SUPPORTED */ 173